The long-term goal of this research proposal is to use x-ray crystallography to study the oxygen-evolving photosynthetic reaction center, photosystem II (PSII). PSII is a membrane protein complex which receives light energy to split water and release molecular oxygen and protons. The reduction of water produces reducing equivalents which PSII transfers to other proteins in the photosynthetic electron transport chain. Eventually, the reducing equivalents help produce NADPH. This structural biology proposal will be fulfilled in three steps. The first step involves generation of monoclonal antibodies to the manganese-stabilizing protein (MSP) which is a part of the photosystem II protein complex. The second step involves utilization of the monoclonal antibodies which bind a part of the complex (MSP) in crystallization screens, in order to produce high-resolution protein crystals of both the PSII complex and MSP alone. As a backup, crystallization trials of PSII using bicontinuous lipidic phases will be performed concurrently.